Alternate Pathways of Bilirubin Metabolism: 1. To determine the bilirubin derivatives (or heme derivatives) formed in: a. Complete deficiency of bilirubin conjugation (the Gunn rat). b. Phototherapy of the Gunn rat and jaundiced newborn infants. 2. To determine: the subcellular fractions, enzymes, and organs involved in the alternate /athways of bilirubin metabolism, under a & b above. 3. To determine effects on bilirubin metabolism in the Gunn rat of various inducers and inhibitors of microsomal hydroxylation and lysosomal peroxidation. Effects of Phototherapy: 1. To determine the effects of phototherapy on the activity of various hepatic drug metabolizing enzymes, and on its content of cytochrome P450. 2. To determine the role of bilirubin photoisomers in the excretion of unconjugated bilirubin, and the formation of bilirubin photoderivatives, during phototherapy of the Gunn rat. 3. To determine whether the stimulator effect of phototherapy on bile acid turnover is due to selective alterations of the plasma-tissue pool, as opposed to the enterohepatic pool of bile acids. Formation of Pigment Gallstones: 1. To develop a chromatographic method for large scale isolation of bilirubin conjugates from bile. 2. To determine the effects of lecithin and calcium on bilirubin solubility in bile. 2. To determine if hepatobiliary beta-glucuronidase can hydrolyze conjugated bilirubin in bile at the physiological pH values of 7.0-7.8. BIBLIOGRAPHIC REFERENCES: Soloway, RD, Trotman BW, Ostrow JD: Pigment cholelithiasis. Gastroenterology Jan. 1977, in press. Trotman BW, Morris, TA 3rd, Sanchez HM, Soloway Rd, Ostrow, JD: Pigment vs. cholesterol cholelithiasis; identification and quantification by infrared spectroscopy. Gastroenterology March 1977, in press.